Characteristics
Safeties are now characterized by having two wheels of identical – or nearly identical – size, and a chain-driven rear wheel. The most popular form of the safety bicycle frame, consisting of two triangles, is known as a diamond frame. A similar but different frame used in safety bicycles is the step-through frame.
Despite the enormous variety of modern bicycles, recumbent bicycles are the only major variety of bicycle which do not use this same basic design.
Read more about this topic: Safety Bicycle